1. Field of the Invention
The present invention is related to safety devices for crane booms. More particularly, the present invention is related to methods and apparatus for limiting the movement of a crane boom. Even more particularly, the present invention is related to a method and apparatus for locking a crane boom control stick in a stationary position.
2. Description of the Prior Art
Cranes are well known in the art as devices for hoisting and moving objects utilizing a movable boom. Many modern cranes use booms operated hydraulically rather than by steel cables. Some modern hydraulic cranes have telescoping booms, while other cranes employ articulated booms. Most cranes are mobile, although some are connected to a stationary base. Most cranes can turn in a complete circle on their base, and the boom can be moved upward and downward, and the end of the boom can be moved toward and away from the base of the crane.
The movement of a crane boom is commonly controlled by a plurality of control sticks. The control sticks are usually mounted on the floor of a cab on the crane in which the operator sits. Usually a single control stick controls the movement of the boom upward and downward, and another stick controls the movement of the end of the boom toward and away from the crane. The control sticks are commonly designed to be grasped by the operator and moved away from the operator and toward the operator in a plane to control movement of the crane boom.
The control sticks on hydraulically-operated cranes are essentially "on-off" switches. Thus, when the control stick is moved away from or toward the operator from the neutral position, the crane member controlled by the control stick will move until the control stick is returned to the neutral position, at which time the crane member will remain in the position to which it has been moved.
It is frequently desirable to limit the movement of crane booms in one or more dimensions. For example, if the mobile crane is working under an electric utility line commonly referred to as a power line, it is desirable to limit the upward movement of a mobile crane boom to a height less than the height of the electric utility line to prevent contact of the boom with the electric utility line. Contact of the boom with the electric utility line can result in death or serious injury to the crane operator and/or destruction of the crane and utility line.
Furthermore, a crane may be located close to a vertical wall or a building or other structure making it desirable to limit the distance the boom may be extended from the base upon which the boom rests. If the boom were accidently extended too far from the base the boom could strike the wall possibly causing damage to the wall, crane, and personnel.
Also, it may be desirable to prevent the crane from turning on its base if the crane is working between two vertical structures. For example, the crane may be working between two parallel walls which the crane boom must avoid.
Mechanisms and assemblies for limiting the movement of cranes and other similar objects are known in the art. Exemplary of the prior art are the following U.S. patents:
U.S. Pat. No. 4,043,253 discloses a boom cylinder stop for the lift cylinders of a skid steer vehicle having an elongated tubular body portion which is mounted on the rod end of one of the hydraulic lift cylinders of a skid steer loader. When the boom of the skid steer loader is lifted, the boom stop is carried outwardly with the rod end of the cylinder, the opposite end of the boom stop dropping into a plane adjacent the rod end of the cylinder when the hydraulic cylinder is almost fully extended. Thus the boom stop is interposed between the outer end of the cylinder body and the rod end of the cylinder to retain such lift cylinder in an extended position under loading conditions. A projection provided at a lower end of the boom stop carries a toggle mechanism mounted on a pivotal connection, the mechanism including a ramp like projection which rotates downward when the cylinder is extended further outwardly to disengage the stop from the cylinder body, the ramp engaging both the cylinder body and the body portion of the stop to slide the body portion of the stop onto the cylinder body when the cylinder is pulled back to a fully retracted position.
U.S. Pat. No. 3,961,685 discloses a ladder working limit based ladder stopping device for a vehicle equipped with a vertically and horizontally swingable and extensible ladder (or a fire engine truck), wherein a working limit of the ladder is preset on the basis of an extended length of the ladder corresponding to a particular vertical angle assumed by the ladder, so that when the combined situation of the vertical angle and extended length of the ladder reaches the preset condition, the operating mechanism for the ladder is automatically returned to its neutral position while actuating a warning device and turning on a marker lamp, the operating mechanism being then operated toward the safety side, whereupon the marker lamp is turned off to indicate that the ladder is now safe.
U.S. Pat. No. 3,561,610 discloses an improved safety device on a crane for preventing the crane boom from falling backward onto the crane cab. A push rod is positioned for engagement with the boom when the boom reaches a substantially vertical elevation. The movement of the rod caused by the upwardly moving boom is multiplied through a system of sticks and imparted to a contact stick which pushes the boom control stick into a neutral position thereby stopping the boom before it moves past the maximum safe elevation.
U.S. Pat. No. 3,092,216 discloses a crane boom retarding and stopping device including a cab and a boom pivotally mounted to the cab, a rail assembly, the rail assembly including a pair of opposed side walls, and base connecting the pair of side walls and a device for connecting the rail assembly to the boom, a carriage slidably mounted along the length of the boom and the rail assembly, a guide device within the rail assembly adapted to guide the carriage along the length of the rail assembly, brake shoes mounted and in opposite relation to one another and adapted to engage the opposed wall members of the rail assembly, a hydraulic pressure device mounted on the carriage and adapted to force the brakes into engagement with the wall members of the rail assembly, a shock rod member, the carriage having a pivotal mounting along its upper surface and adapted to pivotally receive one end of the shock rod member, a triangular gantry member fixedly mounted to the cab of the crane and having a transverse support bar with a mounting device located centrally of the support bar, the mounting device being adapted to engage the other end of the shock rod whereby the shock rod may pivot about the axis of transverse member of the gantry frame, a hoist device for raising and lowering the boom along a vertical plane, hydraulic actuating device responsive to the hoist device whereby when the boom is being maintained stationary at a selected vertical position the hydraulic actuating device will act to apply pressure to the hydraulic pressure device for engagement of the brake shoes to the rail assembly of the boom for supporting the boom at the selected vertical position, the hydraulic actuating device being adapted to respond to the hoist device whereby when the hoist device is engaged for moving the boom upwardly or downward the brake shoe engagement is disengaged by the release of the hydraulic pressure, a spring cushion device mounted at the upper end of the rail assembly to provide a remote cushion stop for the carriage movement.
U.S. Pat. No. 2,529,193 discloses a safety boom stop. In a load-handling machine having a hoist boom and power device for operating the boom including a control circuit device and a boom-hoist control member movable into and out of boom-hoisting position, a limit switch connected to the circuit device and having a power-enabling position and a power-disabling position, the limit switch being normally power-enabling position, a mechanical device controlled by the boom for operating the limit switch to power-disabling position upon the raising of the boom to a predetermined height and for restoring the limit switch to power-enabling position upon the lowering of the boom from its limit position, a manually operable locking-type reset switch connected with the circuit device and having an inactive position and a power-enabling position, and reset switch being normally in inactive position and being manually operated to power-enabling position when the limit switch is in power-disabling position, a mechanical device controlled by the boom for restoring the manually operable reset switch from its power-enabling position to its inactive position upon the lowering of the boom from its limit position, and a third switch connected in circuit with the manually operable reset switch and having a mechanical actuating connection with the boom-hoist control member for rendering the reset switch ineffective to energize the power device while the control member is in boom-hoisting position.